Electrocardiography is a transthoracic (across the thorax or chest) interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body. The recording produced by this noninvasive procedure is termed as electrocardiogram (also ECG or EKG). An electrocardiogram (ECG) is a test that records the electrical activity of the heart.
ECG is used to measure the rate and regularity of heartbeats as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart, such as a pacemaker.
An ECG device detects and amplifies the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heartbeat. At rest, each heart muscle cell has a negative charge (membrane potential) across its outer wall (or cell membrane). Increasing this negative charge towards zero (via an influx of the positive ions, Na+ and Ca++) is called depolarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarization that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through “intrinsic conduction pathways” and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
Usually, more than two electrodes are used and they can be combined into a number of pairs, for example: Left arm (LA), right arm (RA), and left leg (LL) electrodes form the three pairs LA+RA, LA+LL, and RA+LL. The output from each pair is known as a lead. Each lead is said to look at the heart from a different angle. Different types of ECGs can be referred to by the number of leads that are recorded, for example 3-lead, 5-lead, or 12-lead ECGs (sometimes simply “a 12-lead”). A 12-lead ECG is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an ECG, traditionally printed out as a paper copy. 3- and 5-lead ECGs tend to be monitored continuously and viewed only on the screen of an appropriate monitoring device, for example during an operation or while being transported in an ambulance. There may or may not be any permanent record of a 3- or 5-lead ECG, depending on the equipment used.
Several studies show that QRS duration above ˜120 msec is a pathological sign and often correlated with various myocardial diseases. Measuring the duration of QRS complex (ventricular depolarization) in an accurate manner is a challenge, especially for a noisy ECG. Typically, clinicians measure the QRS duration manually on the printed paper ECG or on a monitor screen. Some clinicians use computer based software (SW) for such analysis but the software does not measure duration in real time; the ECG is first recorded and then is post-processed using a dedicated ECG analysis tool (e.g. MAC 1600 Marquette 12SL ECG analysis program from General Electric).
Another system for measuring QRS duration is invasive and intended for pacemakers. Another system uses high frequency components present in the QRS wave, but it does not operate in strict real time since it needs to average several beats.
There are generally two types of existing heart monitors: 1) fitness portable monitors having limited capabilities, such as only heart rate, but not ECG waveform, no pre-alert, and poor QRS detector performances; 2) medical grade monitors which are not really portables although they have good performances and provide pre-alerts. Cost of medical grade equipment such as ECG, EMG (electromyogram), EEG (electroencephalogram) is still prohibitive for consumers. Some existing solutions may have good performances but they are not real time. Some others are portable and real time but show poor performances, such as fitness Heart Rate monitors. Medical grade equipment has reasonable performance and generally operates in real time but they are not compact enough for use as portable equipment and are expensive.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.